This invention relates to a radio communication apparatus having a reception intermediate frequency filter.
In general, a radio communication apparatus using a digital modulation method comprises a reception section having a reception intermediate frequency (IF) filter section. The reception section receives a transmission signal as a reception signal which is transmitted from an additional radio communication apparatus. Furthermore, the reception section comprises an IF section and a demodulating section. The IF section is for converting the transmission signal into an IF signal. The IF signal is filtered into a filtered IF signal by the IF filter section in order to remove a noise from the IF signal. The demodulating section demodulates the filtered IF signal into a demodulated signal.
The IF filter section comprises a reception IF filter and a matching section. The matching section is for use in matching the IF filter to the IF section and the demodulating section.
The matching section has a matched impedance which will be called a circuit constant. Dispersion inevitably occurs in the circuit constant under manufacturing. Similarly, dispersion inevitably occurs in the filter characteristic of the reception IF filter under manufacturing. Furthermore, each of the circuit constant and the filter characteristic may vary on the basis of an ambient temperature.
The IF filter may not match to the IF section and/or the demodulating section on the basis of the variation of the circuit constant and/or the filter characteristic. When such a mismatch occurs in a conventional radio communication apparatus, a receiving sensitivity reduces in the conventional radio communication apparatus. Namely, it is difficult to obtain a high receiving sensitivity in the conventional radio communication apparatus.